The present invention relates to a scroll-type refrigeration compressor.
U.S. Pat. No. 4,477,238 describes a scroll-type refrigeration compressor comprising an impermeable housing delimited by an envelope and containing a fixed scroll and a movable scroll, whereby the movable scroll describes an orbital movement relative to the fixed scroll, the fixed and movable scrolls each being equipped with a spiral wrap, the two spiral wraps being engaged with each other and delimiting at least two variable-volume compression chambers.
According to a first embodiment described in U.S. Pat. No. 4,477,238, each spiral wrap has a stepped portion extending over at least a portion of its length starting from its outer end.
This results in the volume of the two external compression chambers, and hence the displacement of the compressor, being increased. These features thus enable compressor performance to be enhanced.
However, this embodiment requires provision of a recess in the plate of the movable scroll designed to receive the stepped portion of the spiral wrap of the fixed scroll.
In order not to decrease the mechanical strength of the plate due to creation of this recess, it is necessary to increase the thickness of the plate. This thickness increase of the plate increases the weight of the movable scroll and hence its inertia. This increase in inertia translates directly into an increased mechanical load on the hub of the movable scroll and the bearings of the movable scroll drive shaft, which can lead to premature wear of the bearings.
According to a second embodiment described in U.S. Pat. No. 4,477,238, only the spiral wrap of the movable scroll has a stepped portion extending over at least a portion of its length from its outer end. These features obviate creation of a recess in the plate of the movable scroll and hence premature wear of the drive bearing of the movable scroll.
However, this embodiment brings about an asymmetrical pressure change between the two outer compression chambers because the volumes of these two chambers are different. The pressure in the chamber which is delimited externally on the wall of the spiral wrap that has the stepped portion is higher than in the chamber which is delimited externally by the wall of the spiral wrap with no stepped portion.
As a result, there are leakages of fluid between these two chambers and hence reduced performance of the compressor.